Does the setting for domain size make a difference if the units are set to something other than None?
If you go into edit mode and press "n" look in the mesh display area and you'll see an option for displaying the lenths of the edges.  If you scale in object mode the values of the edges don't change. If you scale in edit mode they do. If you scale in object mode, hit Ctrl+A and accept the scale. Now your edge lengths reflects the new dimension. This may be why you see no change when you scale the domain. Just guessing, but I think it may help.